1. Field of the Invention
Aspects of the present invention relate to a battery pack, and more particularly, to a battery pack that does not increase contact resistance against an external impact.
2. Description of the Related Art
Currently, portable electrical/electronic devices, which are compact and light, such as cellular phones, notebook computers, camcorders, and the like, are actively being developed and produced. Accordingly, a battery pack is embedded in the portable electrical/electronic devices so that the portable electrical/electronic devices may operate in a place where a separate power source is not provided. The battery pack currently adopts a rechargeable secondary battery by considering an economical aspect. Representative examples of the secondary battery are a nickel-cadmium (Ni—Cd) battery, a nickel-metal hydride (Ni-MH) battery, a lithium (Li) battery, a lithium-ion (Li-ion) secondary battery, and the like. Particularly, an operating voltage of the lithium-ion (Li-ion) secondary battery is greater, about three times, than the operating voltage of the nickel-cadmium (Ni—Cd) battery or the nickel-metal hydride (Ni-MH) battery, which is frequently used as a power source of portable electronic apparatuses. Also, since the energy density per unit weight is relatively greater, the lithium-ion (Li-ion) secondary battery is being widely used.
The secondary battery, as such, generally uses lithium-based oxide as positive electrode active materials and carbon material as negative electrode active materials. Generally, batteries are classified into a liquid electrolytic battery and a polymer electrolytic battery according to the type of electrolyte. In this instance, the battery using the liquid electrolyte is referred to as the lithium-ion (Li-ion) secondary battery, and the battery using the polymer electrolyte is referred to as a lithium polymer battery.
The secondary battery is formed by electrically connecting a bare cell formed by sealing a can accommodating an electrode assembly and electrolyte, and a protection circuit module. The bare cell charges/discharges electricity using a chemical reaction. The protection circuit module controls charging/discharging of the bare cell and prevents overcharging/overdischarging of the bare cell to protect the bare cell.
When the bare cell and the protection circuit module are connected to form the secondary battery, electrical resistance therebetween is reduced in order to improve charging/discharging efficiency. In more detail, if the electrical resistance between the bare cell and the protection circuit module increases, the charging/discharging efficiency of the bare cell is reduced.
Meanwhile, the secondary battery goes through a reliability test for determining whether the secondary battery is stable against an impact in order to mount the secondary battery in an electronic product after being formed in a pack by integrally connecting the bare cell and the protection circuit module. The battery pack increases the electrical resistance between the bare cell and the protection circuit module due to an external impact. The electrical resistance increases as contact resistance increases in a part where the bare cell and the protection circuit module are connected.